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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script type="text/javascript">
        const users = {
            Alex: {
                email: 'alex@alex.com',
                skills: ['HTML', 'CSS', 'JavaScript'],
                age: 20,
                isLoggedIn: false,
                points: 30
            },
            Asab: {
                email: 'asab@asab.com',
                skills: ['HTML', 'CSS', 'JavaScript', 'Redux', 'MongoDB', 'Express', 'React', 'Node'],
                age: 25,
                isLoggedIn: false,
                points: 50
            },
            Brook: {
                email: 'daniel@daniel.com',
                skills: ['HTML', 'CSS', 'JavaScript', 'React', 'Redux'],
                age: 30,
                isLoggedIn: true,
                points: 50
            },
            Daniel: {
                email: 'daniel@alex.com',
                skills: ['HTML', 'CSS', 'JavaScript', 'Python'],
                age: 20,
                isLoggedIn: false,
                points: 40
            },
            John: {
                email: 'john@john.com',
                skills: ['HTML', 'CSS', 'JavaScript', 'React', 'Redux', 'Node.js'],
                age: 20,
                isLoggedIn: true,
                points: 50
            },
            Thomas: {
                email: 'thomas@thomas.com',
                skills: ['HTML', 'CSS', 'JavaScript', 'React'],
                age: 20,
                isLoggedIn: false,
                points: 40
            },
            Paul: {
                email: 'paul@paul.com',
                skills: ['HTML', 'CSS', 'JavaScript', 'MongoDB', 'Express', 'React', 'Node'],
                age: 20,
                isLoggedIn: false,
                points: 40
            }
        }

const name=Object.keys(users)
//1.统计在线人数
 count=0;
 const arr=[];
    for (let i = 0; i < name.length; i++) {
    if(users[name[i]].isLoggedIn){
       count++; 
       console.log(name[i]);
        
    }
}
console.log('人数'+count);

//2.统计分数大于50的人数
count=0;
for (let i = 0; i < name.length; i++) {
   if (users[name[i]].points>50) {
        count++;
        console.log(name[i]);          
   }
}
    console.log('人数'+count);
//3.查找会MongoDB的人，并打印其名字
const arr1=[];
name.array.forEach( key => users[key].skills.includes('MongoDB') ? arr1.push[key] : arr1 );
console.log('会MongoDB的人'+arr1);
//4.查找同时会：MongoDB Express，React，和Node 的人，并打印其名字
const arr2=[];
name.array.forEach( key => users[key].skills.includes('MongoDB','Express','React','Node') ? arr2.push[key] : arr2);
console.log("会MongoDB， Express，React，和Node 的人"+arr2);
 
var collection = {
    "1275":{
        "album":"依然范特西",
        "artist":"周杰伦",
        "tracks":[
            "听妈妈的话",
            "千里之外"
        ]
},
    "2468":{
        "album":"西界",
        "artist":"林俊杰",
        "tracks":[
            "西界",
            "杀手"
        ]
},
    "3245":{
        "artist":"许嵩",
        "tracks":[ ]
    },
    "5439":{
        "album":"遇见"
    }
}
//1.定义方法更新记录:
//function updateRecords(id,prop,value)
//要求：
//1).如果传入的value是一个空值，表示将该属性删除
//2).传入的prop如果是tracks，则代表添加，其他是修改
//3245 tracks '有何不可'
//3245 tracks ''   -->删
//5439 artist '孙燕姿'
//5439 album '逆光'
 function updateRecords(id,prop,value){
    value==' ' ? delete collection[id,value] : prop=='tracks' ? (collection[id,value]).push[value] : (collection[id,value])=value
 }
updateRecords('3245','tracks','有何不可');
updateRecords('3245','tracks','');
updateRecords('5439','artist','孙燕姿');
updateRecords('5439','album','逆光');

console.log(collection);


</script>

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